The present invention relates to an ignition timing control system for an automotive engine of a motor vehicle and more particularly to a system for decreasing the fluctuation of engine speed at acceleration.
Recently, the ignition timing of the automotive engine is electronically controlled by an electronic control system by using timing data derived from a table storing a plurality of data of ignition timings. When the vehicle is accelerated, quantity of intake air, quantity of fuel and the ignition timing largely and rapidly change so that at the beginning of the acceleration, the engine speed increases with fluctuating. As a result, some parts of the power train of the vehicle are twisted, thereby causing uncomfortable shock and vibration.
Japanese patent application Laid Open No. 59-201971discloses an ignition timing control system where the fluctuation of the engine speed is decreased by controlling the ignition timing. In the system, when the engine speed increases from a threshold value (an average speed of the engine speed), the ignition timing is retarded. To the contrary, when the engine speed decreases, the ignition timing is advanced.
However, in order to prevent a large increase hereinafter called surge, the ignition timing must be largely retarded or advanced, which causes knocking of engine and deterioration of combustion efficiency.